This invention relates to a surveillance apparatus for use in the field of a surveillance system and to a software program for accomplishing the surveillance apparatus through a computer. More specifically, the present invention provides an economical surveillance apparatus that is robust to changes of an imaging environment, and a software program for accomplishing the surveillance apparatus.
Surveillance by using a camera has been conducted recently at various places such as roads, railroad crossings, public facilities, service floors of banks, convenience stores, elevators of apartment buildings, and so forth. The object of surveillance is to prevent accidents and crimes and to quickly take necessary counter-measures.
A surveillance system of public facilities such as electric power, gas supply, water distribution, etc, includes a plurality of surveillance cameras disposed not only indoors but also outdoors. Therefore, guards can grasp on the real time basis the condition of each site through monitor televisions of a surveillance center.
However, the requirement of continuously monitoring pictures from a plurality of surveillance cameras for an extended time is likely to invite xe2x80x9coversightxe2x80x9d due to fatigue of the guards. It is therefore customary to employ a method that generates and reports an alarm sound only when any invading object or any abnormal condition is detected, as a surveillance system enabling the guards to watch and confirm the condition only when necessary. Various sensors such as infrared sensors, door sensors, temperature sensors, etc, have been used for the detection, or a method that directly analyzes the images from the surveillance cameras has been used.
The former has high reliability but involves a high cost because a large number of additional sensors must be installed besides the surveillance cameras. The latter does not require additional installation of specific sensors, hence is more economical. However, the latter is not free from the problem of an incorrect alarm because the camera images fluctuate at places where an environmental change is vigorous, such as outdoors, due to sways of trees, rain and snow, reflection of water surfaces, and so forth.
A surveillance apparatus described in JP-A-5-14893, for example, detects an invading object by comparing a background image generated by a smoothing processing in a time direction with an input image. When the background does not change. Therefore, this type of surveillance apparatus can correctly detect the invading object. However, the surveillance apparatus still involves in principle the problem of excessive detection in an environment where the background incessantly changes, such as outdoors.
An image processing apparatus for surveillance according to JP-A-10-105839 uses a mean value of several past frames as a background image, calculates the difference between the background image and an input image to extract an abnormal image, further calculates its difference from a previous frame and distinguishes an abnormal change from others. Because the background image is generated by the mean image, degradation of the detection sensitivity occurs when an invaded object is contained in the background image.
In addition to the problems described above, the conventional surveillance apparatuses have the problem that when reliability is improved, the cost of production becomes higher, and when the cost is lowered, an incorrect alert increases. It is therefore an object of the present invention to provide an economical surveillance apparatus that is robust to an environmental change, and a software program for accomplishing the surveillance apparatus.
To accomplish this object, the present invention provide a surveillance apparatus including background image memory means for storing a plurality images inputted in a time series, memory means for recording a difference map, for calculating and storing a minimum value (difference degree) of an absolute value of a difference between a plurality of images and an image afresh inputted, for each pixel, and judgment means for judging the existence/absence of an invading body by using the difference.
These and other objects, features and advantages of the present invention will become more apparent in view of the following detailed description of the preferred embodiments in conjunction with the accompanying drawings.